The present invention relates generally to an emissions preservation and collection device. More specifically, the present invention relates to a device for acquiring an accurate sample of emissions in the atmosphere surrounding a seal.
Plants and factories utilize process control devices to control the flow of fluids in processes. Process control valves are used to manufacture consumer articles or goods such as fuel, food, and clothes. Even a medium sized factory may utilize hundreds of control valves and dozens of pumps. Most industrial plants utilize volatile organic compounds (VOC""s) in the processes that produce consumer goods. Nearly all industrial plants experience unwanted emissions of VOCs into the atmosphere. The emissions often escape from unintended sources such as valves, pumps, and plumbing involved in the process stream. Emissions from unintended sources are often referred to as xe2x80x9cfugitive emissions.xe2x80x9d The material being controlled in a process will be referred to herein as a fluid although it may be a gas or a multi-phase media.
Many process control devices have shafts that are rotated to control a parameter of the process. For example, a control valve controls the flow of fluid by changing the position of a valve stem which moves a plug. The valve stem may slide up and down, or it may rotate to change the position of the plug. The valve stem travels in relation to a seal. The seal prevents the process fluid from escaping into the atmosphere or outside world.
In operation, a valve stem may move in relation to its valve seal as frequently as two times per second. In extreme cases the stem may move in relation to the seal as many as fifty times per second. Frequent movement of the valve stem and demanding service conditions such as large temperature fluctuations, harsh process chemicals and abrasive particles near the sealing surfaces accelerate the deterioration of the valve stem seal. Recent improvements in seal material and seal retention has greatly increased the service life of valve stem seals; however, eventually all valve seals deteriorate and leak process fluids into the environment. Thus, the monitoring of control valve seals for leakage has become a concern.
Other process control devices such as pumps also have rotating shafts. Thus, it is common for a seal around a pump shaft to develop a leak. Another sealing arrangement commonly occurring in a factory is a pipe flange or a flexible pipe coupling. Vibration in the piping, and seal deterioration due to age and exposure to elements also creates leaks in a process control system and correspondingly undesirable emissions.
In the past few years, the U.S. Government and foreign governments have become sensitive to the release of undesirable chemicals and compounds into the atmosphere. Correspondingly, the U.S. Government has continued to create and apply tougher standards for preventing the release of contaminants such as VOCs into the environment. The U.S. Environmental Protection Agency (xe2x80x9cEPAxe2x80x9d) is the federal agency that is in charge of creating and enforcing the new legislation.
VOCs are very prevalent in industrial processes. Particularly, benzene, toluene, and 1,1,1-trichloroethane are three VOCs that are commonly utilized in manufacturing The EPA has promulgated regulations specifying the maximum permitted leakage of these VOCs from control valves and from factories generally. To comply with the regulations, a plant manager must create a factory audit procedure. The procedure will include recording VOC leakage measurements and reporting the measurements to the EPA.
To comply with one of the EPA regulations a factory must determine how many valves are leaking and the quantity of chemical being leaked by each valve. If an audit determines that the quantity of leaking valves and amount of VOCs released are under a predetermined limit, then according to the regulations, testing or surveys can be reduced in frequency. This is particularly important for large facilities that can contain, for example, 200,000 survey points. It becomes very costly to maintain a staff to constantly monitor 200,000 locations within a plant. Thus, accurate reporting of minimal leakage, significantly reduces the effort and expense for compliance with EPA regulations.
Because automated emission detection systems are not readily available, most factories are using portable instruments and conducting xe2x80x9cwalk through auditsxe2x80x9d. A walk through audit requires physically visiting, measuring and recording emissions from survey points. This is very inefficient compared to an automated system which does not require a physical visit to the survey point.
In addition to the inefficiency of physically visiting and measuring emission, other problems plague such a system. For example, on a windy day, winds may blow the emission away and the portable measuring device will not detect an emission. Additionally, leakage may be dependent on the position of the valve stem. A worn, pitted or bent stem may not leak in one position but may have a severe leak in another position. A portable instrument takes one measurement while physically present, however an automated system can report emission 24 hours a day.
Portable instruments typically use a sampling probe to transport a small sample of the atmosphere, around the probe tip and adjacent to a small area on the seal, to sensors within the portable instrument. The procedural requirements for using a sample probe includes movement of the probe around the entire circumference of the seal and dwelling where the maximum leakage is detected. Thus, the measurement is made on a small portion of the seal and the xe2x80x9coverallxe2x80x9d leakage is not measured. Additionally, it can be difficult to circle the seal with the sample probe due obstructions such as the actuator frame or bonnet.
Currently automated fugitive emission sensing systems are not prevalent in process control systems. There are a few xe2x80x9cmake shiftxe2x80x9d or primitive installations. These are typically placed on valves subject to the most demanding service. Detection is important because immediate repair of leaking valves minimizes the required audits, and greatly reduces expenditures for EPA compliance. An additional benefit of an automated reporting system includes a more effective early warning system. The automated system can alert a facility operator to an impending seal failure. If the emission is flammable, toxic or hazardous, detection enables preventive measures to be taken before a dangerous situation arises.
There are two basic functions to any emission detection system. First, the system must acquire an accurate atmosphere sample by some sort of acquisition system and then it must process the sample to detect the concentration of the target chemical. It is critical that the acquisition system provide an uncontaminated, uniform and undiluted sample to be analyzed.
A permanent installation of an automated fugitive emission sensor system would minimize the xe2x80x9cmanual surveysxe2x80x9d and usage of portable instruments and increase the accuracy of the measurements. However, permanently installed emission sensors also suffer from inaccurate sample acquisition systems. These installed emission sensors must also contend with sample preservation problems that may occur as a result of air turbulence. Thus, it is an object of the present invention to provide a device to effectively acquire an accurate sample of atmosphere adjacent to a seal, either for a portable instrument or an automated emission detection system to enable a chemical detection system to accurately measure emissions.
Accordingly, it is an object of this invention to provide a low cost and robust fugitive emission collection device;
It is another object of the present invention to provide a highly efficient collection mechanism for acquiring a uniform fugitive emission sample;
It is yet another object to provide a low impedance cavity for capturing a sample of atmosphere in close proximity to a seal and delivering the sample to a emission detection system to determine if fugitive emissions are present.
A fugitive emission collection device for acquiring an atmosphere sample around a seal is provided. The emission collection device is a rigid member that forms a low impedance cavity shaped to overlay the seal. The emission collection device has a conduit having an inlet in fluid communication with the low impedance cavity and an outlet that can be connected to an emission detection system, which is used to analyze the atmosphere to determine if excess emissions are leaking from the seal. In the preferred embodiment the collection device is manufactured in two pieces, which basically consists of a base and a cover. The conduit can be created by initially forming a recess in the mating surface of either the base or the cover before they are assembled together. A more uniform and accurate sample of the atmosphere around a seal can be drawn from the low impedance cavity by a collection device that has multiple inlets equally spaced around and proximate to the seal.